Under present clean-fuel regulations, specifically Mobil
Source Air Toxics II (MSAT II), US refiners must reduce the
benzene content in gasoline to 0.62 vol% on an average annual
basis. This rule went into effect Jan. 1, 2011, for large
refiners; small refiners received deferments until 2015. In Europe and many other countries, a 1
vol% maximum benzene level in gasoline is also in effect. Other
regions are expected to adopt similar clean-fuel regulations.
For refiners, the challenge is to meet these tightening
gasoline specifications for benzene cost-effectively without
significant octane loss.

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In the early 1940's, the U.S. was trying to supply Chinese and U.S. forces in China fighting against the Japanese. The only route was from India over the Himalayas by aircraft. This was called "Flying the Hump'--taking off from sea-level and climbing continuously at full power to 30,000 feet. The engines were failing quickly and many planes and crew were lost (killed) as visibility was often zero in the monsoons. Navigation was by compass, directional gyro and a watch- and all too often was not accurate enough as the planes had to zig-zag back and forth along the mountain slope to gain enough altitude.

Engine failure was caused by pre-ignition brought on by continuous detonation (fuel knock) because the fuel simply was not good enough for the engine's demand.

Cumene (isoproplybenzene) was developed as a high octane (150 +) fuel component and refiners were ordered to make it. Alkylating benzene with propylene using phosphoric acid on quartz rock was the UOP process used.